Method of depositing silver



B. BART METHOD OF DEPOSITING SILVER Feb. 23 1926.

Filed Sept. 23. 1921 INVENT OR Biasr'us fiat/'3' ATTORNEY Patented Feb. 23, 1926.

."BLASIUS BART, OF EAST ORANGE, NEW JERSEY.

METHOD OF DEPOSITING SILVER.

Application filed September 23, 1921. Serial msoaeso.

To all whom it may concern:

Be it known that I,'BLAs1Us BART, a cit zen of the Republic of Switzerland, and resident of East Orange, in the county of Essex and State of New Jersey, have invented certain newand useful. Improvements in Methods of Depositing Silver, of which the following is a specification.

The invention relates in general to a method for depositing, silver on an object to be coated thereby and the invention specifically relates to an improvement in the manner of depositin silver on a mould to form reflectors of t e type in which the formed silver reflecting surface is backed by a strengthening layer of electrolytically deposited copper.

The present inventlon features a perfected method which can be practiced independently of personal skill and independently of any variations of climatic conditions present and in which the resulting product will at all times be uniform.

The primary object of the present invention is to attain a brilliant reflecting surface of uniform high lustre, simulating a highly polished silver surface and to attain this result with a minimum loss of reagents, rapidly, in a manner susceptible of adoption for use on a large commercial scale and capable of being operated successfully by unskilled labor.

Certain refinements of operation have been practiced with advantage, for instance, it has been found that the character of the resulting deposit is controlled to a considerable extent by the temperature of the reaction and the temperature of the mould or other deposit receiving surface and in practicing theprocess herein disclosed a temperature of about F. is suggested.

While it is obviousithat different silver compounds may be used and the different compounds in the solutions may be of varying strength, it is suggested that when silver nitrate is used it be freshly prepared,preferably in a proportion of about "80 grammes of the silver nitrate salt to each gallon of water. If rochelle salts is used as the re ducing substance 40 grammes to the gallon is suggested and if formaldehyde be used the strength is to be regulated so that it will not discolor the silver.-

In spraying or otherwise depositing the mixture onto the surface to be coated care must be exercised so that the deposit is not made too fast and it suggested that the discharge be regulated so that one gallon of the substance be discharged per hour when under a pressure of about two pounds per square inch and projected through a pin hole opening.

.In practicing the lution and its reducing agent are caused to flow in streams into a closed chamber for a limited time sufficient to permit somereducing reaction between the substance but in sufficientto permit a complete reduction of all of the silver present. The partially reduced mixture is then projected onto the object to .be coated in small quantities, preferably. but not necessarily in the form of an extremely fine mist orcloud-likc effect.

The best results are attained by spraying a limited portion of the surface to be covcred, then applying the spray to another adjacent portion and then returning and respraying the previously sprayed portion before the previously sprayed portion has had an opportunity to dry. The action will resemble a gentle. blowing of steam on the mould and when a thin, almost transparent film is laid, the depositing actionat this place is operation the silver sointerrupted for a few seconds and then continued for a few more seconds and again interrupted. Apparently the best results are attained when there is a partial drying, and

, perhaps incidental oxidizing, of each layer this method that the silver deposit be of unusually thin depth. Afterwards a deposit of copper or similar backing material is deposited on the silver coating, preferably by depositing the silver coated mould in an electrolytic tank, but this forms no part of the present disclosure.

Various other objects and advantages of the invention will be in part obvious from the suggestions herein made relative to the improved method and from .an inspection of the accompanying drawings showing a means for practicing the process and in part will be more fully set forth in the following particular description of one particular method of practicing the invention.

Referring to the accompanying drawings there is shown largely in diagrammatic outticing the process featured in this disclosure.

line a suggested form of apparatus for prac- .No. 502,679, entitled Mould for reflectors,

filed September 23, 1921, but it is of course to be understood that the showing is made in connection with the process as described for forming reflectors of the semi-spherical type and any formof mould or in fact any form of object to be coated may be considered as the equivalent of the member 10. Itis understood that at the completion of the process there is a thin layer of metallic silver formed on'the' glass mould disclosed, after which the mould with the thin silver coating thereon is positioned in an electrolytic tank (also shown in dotted outlines) and a deposit of strengthening material such as copperis formed on the rear side thereof. This completes the process after which the copper-backed silver coated article is removed from the tank.

Referring to the instrument for depositing the silver film it is noted from the drawings that it is in the form of an atomizing tool 11 of the two jet type. The tool is pro vided with a handle 12. secured to one side of a mixing chamber 13 which is in the form of a cylindrical barrel. The chamber is supplied from a source of silver nitrate solution through the agency of a flexible pipe 14, and is similarly connected with a source of silver reducing solution, such as rochelle salts, by means of a flexible pipe connection 15. The mixing chamber is provided, at the end opposite the inlet formed at the pipes 14 and 15, with a nozzle 16. The discharge end of the nozzle is provided with a pin hole opening. The nozzle is shown to be curved into an L form so as to direct the mixed substances discharged from the mixing chamber 13 transversely of a stream of compressed air. The air is discharged from the nozzle 17 which nozzle constitutes a continuation of a pipe 18, forming part of the tool 11 and secured thereto by straps 19. The pipe is supplied with air from some suitable air compressor through a flexible connection 20. It will, of course, be understood that the fluids in the ipes 14; and 15 are under ressureand that t e several pipes are provi ed with suitable valve controls as is usual in apparatus of this character. I

The length of the mixing chamber is regulated so as to give an opportunity 'forthe silver solution and its reducing reagent to react to such an extent as will cause a partial reduction of thesilver present while out of contact with the air but the chamber is not so long that a complete reduction is effected before the mixture'is discharged. A chamber about five inches long has been used with satisfaction. It is necessary that the claim mixture in the face to be coate final reducing action takes place in air and at the instant that the reduced silver is con tacting with the mould.

Having thus 1. In the art of coating objects with silver, the process which consists in ejecting a spray of a solution of a silver salt into a closed mixing chamber and out of contact with theair, thereby to retard any incidental oxidation, simultaneously ejectmg into said chamber a spray of a solution of a reducing agent for the silver-salt, maintaining a physical and chemical contact between the e ected sprays of the solutions while confined inrthe chamber for a period of time to permit a partial reducing reaction between the solutions and causing the mixed and partially reduced solutions-to be sprayed in the form of a mist onto the surface to be coated while completing the reducing reaction.

2. In the art of coating objects with silver, the process which consists in mixing a solution of av silver salt with a reducing agent therefor, maintaining the association in the absence of air and for a period of time less'than the period necessary to permit a complete reduction of the silver salt present and spraying the resulting partially reduced substance in the form of a mist and in the presence of air onto the surface of the obect to be coated.

3,- In the art of coating objects with a silver deposit, the process which consists in forming out of contact with air a stream comprising a silver compound and a reducing a ent therefor, maintaining the'stream out 0 contact with air to effect a mixing of the silver compound and reducing agent under conditions which will not favor oxidation and spraying the mixture onto the surof approximatelyt0 F. and spraying the resence of air onto the surdescribed my invention, I

mixing a stream of a silver compound with 4 a stream of a reducing agent therefor while out of contact with air and at a temperature 6. In the art of coating objects with a silver deposit, the process which consists in mixing a stream of a silver compound with a stream of 'a reducing agent therefor while out of contact with air and at a. temperature of approximately 60 F. and spraying the mixture onto the surface to be coated which 139 v v r 1,514,544

' surface has a temperature ofapproximately 60F. 7. In the art of coating objects withsilver deposit, the process which consists in mix-- ing a weak solution of silver nitrate of approximately 80 grammes to" a ga lon ofthe deposition on the object being timed to. effect the same before the reducing. reaction of all the silver present is completed. 0 8. In the artof coating ob ects with silver deposit, the process which consists in mixing a weak solution of silver nitrate, of approximately 80 grammes to a gallon of water, with a reducing agent, 'ma1ntaining the mixing operation first out of" contact with. the air and then spraying the mixture or'itothe object to be coated while continuing the mixing operation in the resence of air the mixture being deposite at a rate oi about one gallon per hour when discharged through-a pinhole opening and under a prelslsure of about two pounds per square H1O I 9. In the art of ver, the process whlch consists in mixing a agent therefor,

for a' period of .time less than the eriod.

' necessary to permit a com lete reduction of the silver salt present an erse an air space while completing the reactionand then causin' theresulting metal lic silver to be receive promptly on the object and approximately at the instant that said reactionhas been completed.

10. In the art". of coating ob'ects',with a silver deposit, the process whic consists in :Tvr, the process which consists in introducforming a mixture of a silver com undand a reducing agent therefor," initia lyrmain tainin the reaction under 'conditlons un-- favora Is to oxidation and until the reaction time favorable to oxidation and utilizing the resulting Ject approximately at the termination of metallic silver to" coat the obsaid reaction.

11. In the 'art'of coating objects with si l-- ver, the process which consists in partially reducing a silver solution under conditions unfavorable to oxidation, completing the 're- -;in .bulk fora causing the resuiting partially reduced substance to travver solution an action under conditions favorable to oxidation, continuing the reaction u to the time the reaction at a. temperature of approximately F.

ver, theprocess which consists in'causinga stream of. a silver solution, and a stream of a reducing reagent therefor to commingle necessary to e set a complete reduction of the silver present and then causmg a rest-ricted amount of said partially reduced etc the reducing reaction rough air to the object bestream to compl while passing t ing-ooated. I Y

:13. In the art of coating objects with silver, the process whichconsists in mixing a 'silversolution -ywith a reducing reagent 12. In the art of coating objects with silperiod oftime less than that therefor both being in relatively small bulk v and for a period of time sufficient to permit a partial reductionof the silver but insufficient to permit a completereduction of the silver present and .causlng the resulting mixture to pass during the continuation of said reducing reaction through a pin hole opening onto the object to be coated. coating objects .with sill 14. In the art'of coating objects with sil ver, the process which consists in mixing a solution of a silver salt. w tha 'reducmgo maintaining the 8SS001Etl0n' silver s utionwith a reducing reagent therefor both being in relatively small bulk and for a period of time sufiicient'to permit -a artial reduction of the silver but insufficient to permit a complete reduction of the silver present and causing the resulting mix- I ture topass during the continuation of'said reducing reaction through a pin hole opening on ton-the object to be coated while maintaming the reaction under tem eraturecon- 'ditions of approximately 609;

. 15. In the art of coating objects withsiling into 'a mixin chamber a stream of a sil-' a stream of a reducing reagent therefor, both supplied in 'relatlvely small bulk, causing the solution and reagent s partially completed and then causing the" 'same to complete the reaction under condito remain in said chamber for a brief period of time and then causing the resultin products to flow'continuously from the c amber through a inhole opening andto fall onto the. object eing covered.

- Signedat New York city in the county of New York and State of New York this 12th 

